An electrolytic capacitor that utilizes a metal having valve action such as tantalum or aluminum is generally widely employed, because compact size and large capacity can be obtained by making the valve action metal used as the anode side counter electrode into a form such as a sintered body or an etched foil to enlarge the surface of a dielectric. In particular, a solid electrolytic capacitor that employs a solid electrolyte as the electrolyte, by virtue of its compact size, large capacity, and low equivalent series resistance, as well as having characteristics such as good processability into chips and suitability for surface mounting, is crucial for allowing a more compact size, higher functionality, and lower cost of electronic instruments.
In this type of solid electrolytic capacitor, generally for application with compact size and large capacity, an anode and cathode foils consisting of a valve action metal such as aluminum are wound via a separator to form a capacitor element, this capacitor element is impregnated with the driving electrolytic solution, the capacitor element is housed in a housing made of a metal such as aluminum or a synthetic resin housing, and this has a sealed structure. Aluminum as well as tantalum, niobium, and titanium etc. are used as the anode material, and the same type of metal as the anode material is employed for the cathode material.
In addition, even though manganese dioxide or 7,7,8,8-tetracyanoguinodimethane (TCNQ) complex are known as the solid electrolyte employed for the solid electrolytic capacitor, a technology (Patent Document 1) exists in recent years that focuses on conductive polymers such as polyethylenedioxythiophene (hereinbelow shown as PEDOT) that has a moderate reaction rate and shows superior adhesion of the anode electrode with the oxide film layer.
Such type of solid electrolytic capacitor that forms a solid electrolyte layer consisting of a conductive polymer such as PEDOT on a wound-type capacitor element is fabricated as below. First, the surface of an anode foil consisting of a valve action metal such as aluminum is roughened by an electrochemical etching treatment in an aqueous chloride solution to form numerous etching pits, and then voltage is applied in an aqueous solution such as ammonium borate to form an oxide film layer that will become a dielectric (chemical conversion). Similarly to the anode foil, the cathode foil also consists of a valve action metal such as aluminum, but only an etching treatment is applied on its surface.
In this way, the anode foil having an oxide film layer formed on the surface and the cathode foil having only etching pits formed are wound via a separator to form a capacitor element. Subsequently, a polymerizable monomer such as 3,4-ethylenedioxythiophene (hereinbelow shown as EDOT) and an oxidant solution are each discharged to the capacitor element that was applied repair chemical conversion, or the capacitor element is immersed in a mixed solution of the two to promote a polymerization reaction inside the capacitor element, and a solid electrolyte layer consisting of the conductive polymer such as PEDOT is formed. This capacitor element is then housed in a closed-end tubular housing to fabricate a solid electrolytic capacitor.